I am setting up a web server for a client. They will be using a web app (PHP/LAMP) that I am building. The server will be sitting within their network locally. There will also be a MySQL database on the same server. The load on the server will only be 20-25 concurrent users, but uptime and performance is still very important.
The application itself will be using a back-end CMS (TBD) to display content to the user using JQuery on the front-end and PHP on the back-end.
So, my question is: Is there a good set of server system requirements in terms of CPU, Cache and memory (size/type) to provide a relatively cheap solution, but still provide quality performance.